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Speed is the magnitude of velocity (a vector), which indicates additionally the direction of motion. Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph).
The figure shows a man on top of a train, at the back edge. At 1:00 pm he begins to walk forward at a walking speed of 10 km/h (kilometers per hour). The train is moving at 40 km/h. The figure depicts the man and train at two different times: first, when the journey began, and also one hour later at 2:00 pm.
Speed, the scalar magnitude of a velocity vector, denotes only how fast an object is moving, while velocity indicates both an object's speed and direction. [3] [4] [5] To have a constant velocity, an object must have a constant speed in a constant direction. Constant direction constrains the object to motion in a straight path thus, a constant ...
The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading. The indicated speed must not be more than 110 percent of the true speed plus 4 km/h (2.5 mph) at specified test speeds.
Metre per hour (American spelling: meter per hour) is a metric unit of both speed and velocity (Vector (geometry)). Its symbol is m/h or m·h −1 (not to be confused with the imperial unit symbol mph). By definition, an object travelling at a speed of 1 m/h for an hour would move 1 metre.
The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). [1] It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). [2] The corresponding unit in the International System of Units (SI) is the meter per second.
The benz, named in honour of Karl Benz, has been proposed as a name for one metre per second. [10] Although it has seen some support as a practical unit, [11] primarily from German sources, [10] it was rejected as the SI unit of velocity [12] and has not seen widespread use or acceptance.
To help compare different orders of magnitude, the following list describes various speed levels between approximately 2.2 × 10 −18 m/s and 3.0 × 10 8 m/s (the speed of light). Values in bold are exact.